The present invention relates to a method for repairing vanes for gas turbine engines, and more particularly to a method suitable for repairing high pressure turbine (HPT) nozzle segments for gas turbine engines.
Over time, components of gas turbine engines are prone to damage and wear. Components in the “hot” section of the engine are particularly prone to damage brought on by high temperature and pressure conditions. The high pressure turbine (HPT) nozzle segments, which are vane structures located immediately aft of a combustor in many gas turbine engine designs, are components that can experience a significant amount of corrosion and wear problems. However, replacing damaged parts like the HPT nozzle segments with entirely new replacement parts is expensive. It is desirable from a cost savings perspective to salvage or reuse existing components where suitable repairs can be made. However, component geometries may make repairs to some portions of the component impossible without cutting the component into pieces (to provide access to otherwise inaccessible portions of the component), repairing it and then reassembling it. In addition, some types of corrosion cannot be removed from a component without creating unrepairable “potholes”.
A number of existing methods are known for repairing vanes of a high pressure turbine (HPT) nozzle segment of a gas turbine engine. For example, U.S. Pat. No. 3,182,955 to Hyde states that it was known in the art to cut apart adjacent vane or blade segments (i.e., vane or blade singlets) in order to replace a damaged singlet with a new replacement part. U.S. Pat. No. 4,176,433 to Lee et al. discloses cutting apart two vane segments (or vane clusters), salvaging two halves of the respective segments, and then joining two salvaged halves of the vane segments to form a salvaged vane segment in the original configuration (i.e., blueprint configuration). Furthermore, U.S. Pat. No. 6,785,961 to Caddell, Jr. et al. discloses a repair process essentially identical to those of Hyde and Lee et al. that uses a newly manufactured singlet joined to a salvaged vane singlet (i.e., half of an original vane segment structure).
While methods of cutting apart vane segments and joining the salvaged half (i.e., singlet) with a new or salvaged singlet are known, existing methods do not disclose reliable methods for precisely aligning the airfoils of the repaired vane segment at original blueprint specifications. The cutting and joining process can add variations and increase dimensional tolerances to a point where the alignment of the airfoils of a repaired vane segment are less than optimal (e.g., throat dimensions between adjacent airfoils), which can lead to undesired engine performance losses. In particular, datum surfaces of the original part that determine the mounting alignment of the part in an engine can be effectively destroyed through repair processes that add material to the damaged component, as well as through the process of cutting apart and rejoining halves of a component to effectuate necessary repairs. Thus, it is desired to provide an improved vane segment repair method that facilitates more precise tolerances and vane segment subcomponent positioning.